Precipitation hardened austenitic ferrous base alloy article

ABSTRACT

A PRECIPITATION HARDENED ARTICLE FORMED FROM AN AUSTENITIC CR-NI-MO-TI FERROUS BASE HIGH TEMPERATURE ALLOY OF A TYPE DESIGNATED AS A-286 (AISI 660) CONTAINING 1.62.3% TITANIUM, 0.10-0.30% SILICON AND 0.15-2% MANGANESE.

Patented Mar. 5, 1974 3,795,552 PRECIPITATION HARDENED AUSTENIIIC FERROUS BASE ALLOY ARTICLE Wesley R. Kegerlse, Oley, and Donald R. Muzyka and Peter R. Barbis, Reading, Pa., assignors to Carpenter Technology Corporation, Reading, Pa.

No Drawing. Continuation-impart of abandoned application Ser. No. 743,621, July 10, 1968. This application Apr. 14, 1971, Ser. No. 134,028

Int. Cl. C221: 39/14, 39/20 US. Cl. 14837 5 Claims ABSTRACT OF THE DISCLOSURE A precipitation hardened article formed from an austenitic Cr Ni-Mo-Ti ferrous base high temperature alloy of a type designated as A-286 (A181 660) containing 1.6- 2.3% titanium, DAG-0.30% silicon and 0.152% manganese.

This application is a continuation-in-part of our patent application filed July 10, 1968, Ser. No. 743,621 now abandoned.

This invention relates to precipitation hardened articles formed from an austenitic CrNi-Mo-Ti ferrous base high temperature alloy hitherto manufactured and sold under the type designation A151. 660 and identified in the trade as A486 alloy. More specifically, this invention relates to the provision of such articles having a unique improvement in the stress rupture strength and ductility which is unexpectedly provided by a drastic reduction below a critical value in the amount of silicon hitherto considered a necessary part of the alloy, and the improvement in stress rupture strength is further enhanced by also reducing the manganese content of A-286 alloy below a critical value.

A-286 alloy prior to this invention contained by weight a maximum of 0.10% carbon, 1-2% manganese, 0.44% silicon, 13.5l6% chromium, 24-28% nickel, 14.75% molybdenum, l.62.5% titanium, (ll-0.5% vanadium, a maximum of 0.35% aluminum, 0.001-0.0l% boron and the balance iron except for incidental impurities. The alloy has been made and sold in relatively large quantities for use at temperatures up to about 1300" F. with good results where high strength and good corrosion resistance Was required. Because of its stress rupture strength and notch rupture ductility, the alloy has come to be accepted by jet engine manufacturers for use in making jet engine parts such as turbine discs, blades, frames, casings, after burner parts and bolts which in use are subjected to stress at elevated temperature. The alloy derives its desirable properties from the combined effects of solid solution strengtheners, chromium and molybdenum, and precipitation strengtheners in the form of a nickel-titanium precipitate identified as Ni Ti.

Hitherto, when better tensile properties and, particularly better high temperature stress rupture strength were required than could be provided by the A-286 alloy, it was considered necessary to increase the amount of strengtheners present in the alloy if the requirements to be met were not so severe as to warrent the substantial increase in cost usually associated with the substitution of larger proportions of nickel for iron. "For example, A.I.S.I.

type 663, usually designated type V-57, contains about 3% titanium as compared to the close to 2% titanium usually present in A-286. However, though capable of substantially greater strength than A-286, the V-57 alloy has not enjoyed the wide acceptance accorded the A-286 alloy, largely because of its tendency to be more brittle and notch sensitive than A-286 as would be expected from its larger titanium content, and because of the greater difiiculty encountered in forging the alloy. Furthermore, efforts to overcome those difficulties by reducing the silicon content in V-57 alloy to prevent the formation of G-phase, though to be the cause of the h t working difficulties, have not proven to be entirely successful in overcoming the resistance to wider acceptance of the alloy.

As brought out in US. Pat. No. 3,065,067 to Aggen 1 and iong been the understanding of the art, at nominal 2% titanium level (about 1.6-2.5% Ti) characteristic of .A-286 alloy, a substantial amount of silicon in excess of about 0.4% was required to obtain the best all-around properties, particularly the best high temperature stress rupture ductility. And this was believed to be the case whether the alloy was solution treated at about 1650 F. near the lower end of the useful solution treatment temperature range or at about i950 F., near the upper end of the useful solution treatment temperature range.

It is therefore a principal object of this invention to provide precipitation hardened articles formed of A-286 alloy having improved stress rupture strength and ductility without adversely affecting their other desirable properties or their cost of manufacture or fabrication.

The objects and advantages of the present invention can be attained by carefully controlling the titanium content and maintaining both the silicon and manganese contents of the alloy, so as to keep them in very narrow ranges. In accordance with the present invention, the titanium content is maintained within the range of 1.643%, preferably 13-23%. The silicon content is at least 0.10%, preferably at least 0.15% and no more than 0.30% preferably no more than 0.25%. The manganese content is at least 0.15%. While up to about 2% manganese can be tolerated, best results are obtained with no more than 0.40%. With the elements titanium, silicon and manganese thus controlled, the stress rupture ductility of the alloy as measured by percent reduction in area of a specimen is improved two fold when tested to rupture under a load of 65,000 psi. at 1200 F. This increase in stress rupture ductility is accompanied by a significantly improved stress rupture life which can approach 200 hours or more. Reduction of the manganese content of the alloy to the preferred amount of 0.15-0.40% alone does not appear to have any effect upon the stress rupture ductility of the alloy as measured by percent reduction in area. Furthermore, with silicon in the neighborhood of 0.4% or more, such reduction of the manganese content of the alloy appears to have an erratic effect on stress rupture life of the alloy and, if anything, detrimentally effects that property. Once the silicon content of the alloy is reduced below 0.35%, the manganese content of 0.l5-0.4% has the surprising effect of increasing the stress rupture life.

1 See Aggens Heat No. UMV-fi in Table II illustrating A- 286 alloy (though not so identified) and the accompanying discussion in col. 6. See also Aggens Heats Nos. -056 A-E, Tables IV-VI.

Broad Preferred range range Carbon 1 0. 10 1 0. 08 Manganese. 0.15-2 15 0. 40 Silicon 0.10030 0 15-0. 25 (hromium 13. 5-10 13.5-16

Nickel I 1 24% 24-28 Molybdenum l-l. 75 l-1.T5 Titanium. 1. 6-2. 3 1. El-Q. 3 Vanadium 0.1-0.5 0105 Aluminum. I 0.35 1 0. 35 Boron 0.0014101 0. 00190.01

1 Maximum.

The balance is iron except for incidental impurities which may also include phosphorus up to a maximum of 0.04%, sulfur up to a maximum of 0.03% and copper up to a maximum of 0.5%. It is to be noted that by the foregoing tabulation it is not intended to restrict the preferred ranges for use solely in combination with each other. Thus, the preferred quantity of 0.l50.25% silicon can be used with the broad ranges of any or all of the elements carbon, manganese, titanium and boron; also 0.100.25% silicon can be used and 0.15-0.30%.

In practice, the alloy is prepared by melting and casting an ingot which is then used as a consumable electrode and remelted for best results. The examples of the present invention set forth in Table I were prepared as 17 pound vacuum induction beats and are arranged according to their silicon contents. Exs. 1 and 5 and Exs. 2 and 4 were prepared as split heats to facilitate varying the silicon and manganese contents while minimizing variations in the remaining elements. Exs. 1-6 each had the composition indicated, the remainder being iron and incidental impurities.

TABLE I Example No.

.053 .040 .054 .054 .041 1. 3a .23 1. 31 .20 .23 .14 .25 .27 .25 .20 .021 021 022 .024 .021 .033 .003 001 .005 .002 14. 42 14. a0 14. as 14. 75 14. 43 25. 00 24. 52 25.14 25. 24. 73 1. 1. a0 1. 27 1. 20 1. 29 2.12 2. 01 2.12 2.17 1. 0s .18 .14 .15 .15 .17 .21 .25 .21 .21 .20 .29 .23 .20 .31 .25 .0071 .0055 .0007 0000 .0052

Each of the ingots having the composition indicated in Table I was forged from a furnace temperature of 2050 F. to a inch bar from which the required test specimens were formed to provide two tests of the properties indicated in Tables II and III below.

All of the test specimens were subjected to the same heat treatment. They were heated for one hour at 1800 F., oil quenched, then heated for 16 hours at 1325 F. followed by cooling in air. Examination of the microstructure of the test specimens showed that they all had an equivalent grain size of about ASTM 7-8.

Smooth bar specimens used in carrying out measurements of 2% yield strength (2% Y5), ultimate tensile strength (UTS), percent elongation EL), and percent reduction in area RA) at room temperature (70 F.), had a gage diameter of .252 in. and a gage length of l in. The results of these tests are listed in Table II, .2% Y8 and UTS being in units of 1,000 p.s.i.

TABLE 11 Ex. No. M11 51 YS UTS E1. RA

1 2- 4 105.2 165.5 28.3 49.0 b 1 i 103.2 151.0 28.4 52.4 2 L 33 10s. 2 105. 1 24. 2 45. s r 100. 2 155. 0 2r. 0 45. 6 10. 5 15a. 0 2a. 4 01. 4 3 i 112. 5 150. 7 2s. 0 55. s 1m. 2 150. 5 25. 4 50. 2 l 31 E 105. 3 150. 5 2s. 2 5a. 5 1 v 107.7 154.5 25.0 45.0 5 1 102. 2 155.1 27. 4 40. 0 5 t 112. 0 150. 1 20. 3 55. 8 l 111. 7 150. a 25. 4 55. 5

Combination smooth/notch test specimens were also formed having a smooth bar gage diameter of .178 in. and a gage length of .712 in. The notch portion of each of these specimens had a notch diameter of .178 in., a major diameter of .252 in., and a notch root radius of .005 in., giving a stress concentration factor (K,;) of about 3.8. The combination smooth/notch specimens were subjected to a test load of 65,000 p.s.i. at 1200 F. with the stress rupture life in hours, percent elongation and percent reduction in area indicated in Table III.

TABLE III Ex. No. Mn 51 Life thrs.) El RA l 31113 21:3 33 l i511? 22:3 iii; 5:? 233% l 123:5 $1? 2533 325:3 ii? 2.11%, 23 130. 2 24. 0 40. 1 l 131. 7 3'2. 9 49.1

Examples 1-6 demonstrate the improved stress rupture ductility as measured by percent reduction in area characteristic of this invention. None had notch failures. Also, with manganese between 0.l50.40% as in Examples 1 and 5, improved stress rupture life is provided. Examples 3 to 6 also have less than 0.40% manganese, but their respective 2.01% and 1.98% titanium content is sufliciently below that of the other examples to account for the shorter stress rupture life obtained.

The following Examples 7-14 are outside the scope of this invention and are presented for purposes of comparison to demonstrate the criticality of the stated amounts of manganese and silicon which must be maintained if the benefits of the present invention are to be attained.

Ingots having the composition of Examples 7-14 were prepared as was described in connection with Examples l-6 and having the compositions in percent by weight indicated in Table IV. As in Table I, the remainder was iron except for incidental impurities.

TABLE IV Example No.

14. 25 14. 37 13. 03 13. 98 14. 14. 35 14. 71 14. 71 24. 63 24. 75 24. 24 24. 23 24. T6 24. 78 25. 53 25. 5B 1. 25 1. 28 1. 25 1. 25 1. 29 1. 29 1. 33 1. 33 2. 24 1. 08 2. 22 2. 20 2. 27 2. 26 2. 32 2. 32 151 1T .15 .15 .15 .14 10 .17 .27 25 .24 .25 .25 .25 .20 .27 .25 .20 27 .27 .30 .31 .31 .32 .0052 010 0063 .0062 .0068 .0060 .0008 T2 The ingots were hot worked to form bars from which room temperature tensile specimens and elevated temperature combination smooth/ notch stress rupture specimens were formed, heat treated and tested; all as was described in connection with Examples 1-6. The results of the room temperature tensile tests are set forth in Table V (2% Y5 and UTS being in units of 1,000 p.s.i.), and the results of the stress rupture tests carried out at 1200" 'F. under a load of 65,000 psi. are set forth in Table VI. As in the case of Tables II and III, the manganese and silicon contents of the examples are repeated for convenience.

TABLE v Mn s1 2% Y8 UTS El. ,7, RA

105 104 25 -10 10 10a 10a 2s .50 23 43 113.7 158.1 22. a s4. 5 11a. 7 150. 1 20. 2 5s. 8 22 46 107.8 157. a 20. 1 5s. 2 111.0 100.3 25.7 45.0 37 45 100.2 100.1 23.2 40.0 109.1 100.0 25.0 51.2 15

TABLE VI M11 51 Life (1112.) El. RA

101.2 18.5 22.0 is as re 21 5. -2 iii 14s. 100.7 12.2 13.3

Examples 7 and 8 demonstrate how sharply critical the manganese and silicon ranges are in the alloy of this invention. With insutficient manganese and silicon, that is 0.052% of each, the stress rupture ductility as meas ured by percent reduction in area characteristic of this invention is not attained. This is also the case when, as in Example 8, there is too much silicon present. Examples 9-14 show the continuing adverse effect of the increasing silicon contents on the alloys stress rupture ductility as measured by percent reduction in area. Example 12 will be recognized as falling well within the accepted range for A-286 alloy as it has hitherto been made and sold. The test results obtained from the specimens of Example 12 can be directly compared to those obtained from the other examples set forth herein because all of the metal and test specimens were prepared in the same way, had the same heat treatment and grain size, and were tested under the same conditions. Consideration of the test results in Table VI makes it clear that reduction of the manganese content of A-286 alloy, without reducing the silicon content below 0.35%, has no significant elfect upon the stress rupture ductility of the alloy as measured by either percent elongation or percent reduction in area. Moreover, without controlling the silicon content in accordance with this invention, reduction of the manganese content from 1.24% in Example 12 to 0.22% in Example 9 does not benefit the stress rupture life of the alloy and may have an adverse elfect thereon. On the other hand, as is demonstrated by the data set forth in Table III, with the silicon content ranging from (HO-0.30% and even with as much as 1.33% manganese present, there is a sharp increase in the stress rupture ductility of the alloy as measured by percent reduction in area. And at that low level of silicon, for a given titanium level, reduction of the manganese content, in accordance with the preferred embodiment of this invention, unexpectedly has the effect of further increasing the stress rupture life of the alloy.

As a further demonstration of the improved properties attainable in accordance with the present invention, 2 test specimens of Example 3 were prepared as described hereinabove but were solution treated at 1950 F. instead of 1800 F. When sruhiected to a load of 65,000 psi. at 1200 F., they gave a stress rupture life of 711.3 hours and 755 hours with 19.8 and 19.3 percent elongation and 54.6% and 46% reduction in area. These tests show a unique combination of stress rupture life and ductility at I200 F.

It may also be noted from a comparison of the data in Table II with the data obtained from Example 12 in Table V, that not only is the stress rupture life and ductility of our alloy as measured by percent reduction in area at elevated temperatures improved, as was seen, but also the remaining properties of our improved alloy are comparable to those obtained from the standard A286 alloy composition of Example 12.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. A precipitation hardened article for use under stress at temperatures up to about 1300 F. having good stress rupture life and ductility when subjected to a stress of 65,000 p.s.i. at a temperature of 1200 F. and formed from an austenitie chromium-niclrel-molybdenurn-titanium ferrous base alloy which consists essentially by weight of a maximum of 0.1% carbon, about (HS-2% manganese, about 0.104130% silicon, about l3.5-l6% chromium, about 24-28% nickel, about 1-1.75% molyb denum, about 1.62.3% titanium, about 0.10.5% vanadium, up to 0.35% aluminum, about 0.000001% boron, the remainder being iron except for incidental impurities, said alloy being strengthened by a Ni Ti precipitate.

2. As precipitation hardened article as set forth in claim 1 in which said alloy contains no more than about 0.40% manganese.

3. A precipitation hardened article as set forth in claim 2 in which said alloy contains at least about 0.15 70 silicon.

4. A precipitation hardened article as set forth in claim 3 in which said alloy contains no more than about 0.25% silicon.

5. A precipitation hardened article as set forth in claim 3 in which said alloy contains no more than about 0.08% carbon, at least about 1.9% titanium, and at least about 0.003% boron.

References Cited UNITED STATES PATENTS 2,801,916 8/1957 Harris 128 F 2,879,194- 3/1959 Eischelberger 75128 F 3,065,067 11/1962 Aggen 75-128 V 3,212,884 10/1965 Soler 1 75128 V 3,300,347 1/1967 Kasza 75128 F HYLAND BIZOT, Primary Examiner US. Cl. X.R.

75-428 T, 128 V, 128 W UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent @795552 Dated Marsh is 1974 Wesley R. Kegerise, Inve t Donald R. Mugvka. and Peter B. Barbie It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 12, for "though" read thought Column 4, line 42, after "3, for "to" read and Column 4, Table IV, for Cu, under Example 9, for "27" read Column 5, Table VI, Example 14, under %RA,r for "24.5" read Column 6, line 44, in claim 2, for "As" read A Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM P uscomwoc 6O375-P69 U S GOVERNMENY PEFHYING OFFICE 969 0-365-33i Dedication 3,795,552.--Wesley R. Kegerse, Oley, and Donald R. Muzyka, and Peter 1?.

Barbie, Reading, Pa. PRECIPITATION HARDENED AUSTEN- ITIC FERROUS BASE ALLOY ARTICLE. Patent dated Mar. 5, 1974. Dedication filed J an. 10, 1980, by the assignee, Garpenter Technology Corporation. Hereby dedicates to the Public the remainder of the term of said patent.

2;; Gazette, Apm'l 8, 1.980.] 

